linux-kernel - Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace on i386

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Message-ID: <20190723151447.GO3419@hirez.programming.kicks-ass.net>
Date:   Tue, 23 Jul 2019 17:14:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [5.2 REGRESSION] Generic vDSO breaks seccomp-enabled userspace
 on i386

On Tue, Jul 23, 2019 at 07:04:46AM -0700, Andy Lutomirski wrote:
> 
> 
> > On Jul 23, 2019, at 2:18 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> >> On Mon, Jul 22, 2019 at 04:47:36PM -0700, Andy Lutomirski wrote:
> >> 
> >> I don't love this whole concept, but I also don't have a better idea.
> > 
> > Are we really talking about changing the kernel because BPF is expecting
> > things? That is, did we just elevate everything BPF can observe to ABI?
> > 
> 
> No, this isn’t about internals in the kernel mode sense.

*phew*, I was scared for a wee moment.

> It’s about the smallish number of cases where the kernel causes user
> code to do a specific syscall and the user has a policy that doesn’t
> allow that syscall.  This is visible to user code via seccomp and
> ptrace.
> 
> Yes, it’s obnoxious.  Do you have any suggestions?

Not really; I think I just demonstrated I don't fully understand the
problem space here :/